1. Field of the Invention
The present invention relates generally to cutting tool inserts of the type utilized in the drilling, mining, and construction industries. In particular, the present invention relates to improvements in wear resistant inserts which are adapted to be installed on the face of a cutting tool and which are formed of particles of carbide or other highly abrasive material sintered in a binder of cobalt or other less abrasive, but tougher metal.
2. Description of the Prior Art
In the drilling of oil and gas wells, drill bits are installed at the lower end of a rotary drill string for cutting through rock and other hard formations. These bits, which may, for example, be of a tri-cone rotary type or a percussion type, have inserts of wear resistant material installed on the cutting faces of the bit by press fit or by being cemented in place such that their outer ends project from the face of the bit body to provide the wear surfaces of the bit.
The inserts are available in different "grades" depending on the particle sizes and/or chemical composition, whereby the user is able to choose between relatively hard, but more brittle, or less hard, but tougher, inserts. The wear surfaces on the outer ends of the inserts are so contoured to define a tip. These surfaces may be rounded or conical with the tip located in the center of the outer end of the insert (dome-type), or, depending on the use to which the bit is to be put, may be flat along opposite sides of a tip which extends laterally across its outer end (chisel-type). As the insert is worn, the tip forms flats which dull the cutting surfaces of the insert. As a result, the cutting rate of the insert is reduced and/or it may be necessary to prematurely remove the bit to permit the inserts to be replaced or resharpened.
Dual component inserts having a harder, more wear resistant portion and a less hard, but tougher portion have been made by positioning the different types of hard metal so that more of the tougher type is brought into the cutting surface of the insert as the cutting insert wears away. Such inserts are comprised of different zones or layers having variations in resistance to wear and in toughness. See U.S. Pat. Nos. 2,842,342, 2,888,247, and 2,889,138, for examples of such inserts. Such inserts tend to wear unevenly, reducing the effective life of the insert. Furthermore, such inserts require piecing the inserts together by brazing or during the sintering process. Other inserts in the prior art employ a relatively thin layer of a harder grade of tungsten carbide on a relatively thicker base of a tougher carbide material as disclosed in U.S. Pat. No. 4,705,124. The harder grade of tungsten carbide forms the earth engaging face of the insert. The useful life of these rock bit inserts is limited by the relative thickness of the harder carbide material, with the effectiveness of the inserts being greatly reduced once the harder material has been worn to a blunt surface or completely removed by wear or fracturing during drilling.
Inserts having two or more components meeting at a mating plane are known as provided in U.S. Pat. No. 4,722,405. The insert is oriented in a cutting tool so that the tougher component is on the leading face of the insert, and the harder component defines the trailing face. Again, the insert tends to wear unevenly thereby reducing drilling efficiency as the harder carbide component is worn away.
It is therefore an object of this invention to provide a dual component insert which is of such construction that there is less tendency for it to become dull as it wears.
It is another object of this invention to provide a dual component insert which is of such construction that there is less tendency for it to wear unevenly.
These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of the attached drawings and appended claims.